“I came from the country, and when I came to the city, I was ridin’ high, you know. I was seeing more lights than I ever dreamed to shine in the world. ‘Cos where I came from, there wasn’t too many lights. Bugs made a lot of light, but after that there wasn’t no lights.” -John Hunter

John Hunter should have been at a higher latitude! Because if you’re fortunate, at a high enough latitude (either north or south), the following sight will sometimes greet you in the night sky.

Image credit: Thundafunda.com.

In the northern hemisphere, we call it the Aurora Borealis, while the southern gets the Aurora Australis. From the Earth, it looks like great multicolored ribbons slowly moving across the sky, while from space, you can clearly see that something interesting is going on in Earth’s atmosphere.

Image credit: International Space Station.

From this angle, it’s pretty clear that something’s going on from above. In other words, something’s coming in from space to strike the Earth’s atmosphere, producing this great display of lights.

Can we zoom out even more, you ask?

Image credit: NASA's IMAGE satellite.

Of course we can! The Aurora Australis, as photographed here by NASA, can make a spectacular “ring” pattern as seen from above. The Aurorae aren’t unique to Earth, either. We’ve seen them on many other planets, including Saturn (below).

Image credit: Hubble Space Telescope.

So where do they come from? Believe it or not, the Sun! The incredible temperatures and energies of the Sun not only ionize matter, but send these charged particles hurtling through space towards us at thousands of kilometers per second!

How will we ever survive?!

Image credit: NASA.

Well, thankfully, here on Earth we’ve got a great magnetic field! And one of the wonderful things about magnetic fields is that they bend charged particles, which means that — for the most part — our own planet deflects this radiation from the Sun safely away from Earth!

Except, that is, near the North and South magnetic poles, where those field lines all appear to enter/exit our planet. And whenever the Sun emits a flare, prominence, or other “event,” here’s what happens.

Image credit: NASA's Marshall Space Flight Center.

The North and South magnetic poles act as funnels, pulling charged particles into the upper atmosphere in a ring around the magnetic poles! These particles come in, and are energetic enough that they knock electrons off of their atoms in the atmosphere!

Image credit: International Atomic Energy Association.

Those electrons then recombine with atoms, producing the spectacular light show in that beautiful ring-like pattern we saw above. And at high enough latitudes, parts of that “ring” become visible to human eyes, and that’s what you see as the aurorae!

Last week, there was a spectacular show, and it was captured at high northern latitudes by many amateur and professional photographers.

Image credit: Will Gater, who has more images of Aurora hunting in Finland at willgater.com.

We normally think of aurorae as these static ribbons in the sky, but taking a look at a time-lapse of them, you can see that nothing could be further from the truth! I hope you enjoyed this stunning look at the most beautiful natural light show the world has to offer!

So where do they come from? Believe it or not, the Sun! The incredible temperatures and energies of the Sun not only ionize matter, but send these charged particles hurtling through space towards us at thousands of kilometers per second!

This is a common myth.

Particles in the solar wind (which generally has speeds of 300 to 800 km/s; higher speeds only occur in events known as coronal mass ejections, which affect the location of auroral displays, but aurora can still occur without them) only have direct access to Earth in two narrow regions, one in each hemisphere, known as the cusps. See, e.g., Chapman and Ferraro (Terrestrial Magnetism and Atmospheric Electricity 36:171, 1931). The particles which cause the visible aurora in the rest of the auroral oval come from the magnetosphere, not directly from the sun. Those particles frequently do have speeds of thousands of km/s due to acceleration above the aurora.

Some of Jupiter’s auroral features are tied to the Galilean satellites: there are bright spots at their magnetic footpoints. Io especially is a major source of plasma.

I moved to Anchorage just over a year ago, but missed last week’s display. I can’t wait to get a chance to see them.

Something I learned at the Fairbanks Science Center’s Aurora display is that the northern and southern lights mirror each other, as electrons zip back-and-forth along the same field line. I found that fascinating.

Eric
“The particles which cause the visible aurora in the rest of the auroral oval come from the magnetosphere, not directly from the sun.”

It is my understanding that a situation called preconditioning is involved.(a condition that must exist before something can occur).

Northward IMF drives efficient capture of solar wind plasma triggering formation of superdense and cold plasma sheet material.If southward IMF closely follows, this material is delivered into the inner magnetosphere, acts as a source of population for the ring current, and produces a more intense storm.
Source Thomsen et al 2003

The ring current acts as a buffer and a source, it also has a coupling feature as it has a mixture of solar and ionospheric ions.The histories of particle precipitation is relevant to the development, so in this respect I guess one could say (not a direct link) yet it is not disconnected either.

David, it’s proximity to magnetic north. As Ethan wrote, they occur “near the North and South magnetic poles, where those field lines all appear to enter/exit our planet.”

Now combine this with what the magnetic field looks like while the Earth’s magnetic field is flipping, and you’d get aurora all over the place, but still in specific sorts of ways. While a seafaring civilization may not think magnets were very useful for navigation, but they might notice that a “compass” would point toward centers of aurora rings.

anything new about why/if we can hear them?i have,i was roused out of my tent on a remote lake in Canada by the buzzing.it was a major display and just not green haze.other times massive blinking reds and green displays were quiet.

Question: What gives Earth or some other planets/stars magnetic fields? I know Earth’s magnetic field is mostly due to its molten core. But there are planets that do not have a liquid core, but they have a magnetic field. There are also planets without magnetic fields. Why?

The Northern Lights are beautiful, but can ruin naked-eye astronomy. Imagine a perfect night without a moon or even a hint of haze. You are planning on viewing some faint object -and then the aurorae come out, lighting up the place like the full moon!

@SphereCoupler: Yes, there are lots of details, more than I could fit in a comment on a blog post. Entire books have been written on the subject, and I own some of those books.

The question of whether a change in IMF direction is needed to trigger a substorm is a current controversy in the field. I have seen papers in the last few years that argue both sides of the question. It’s a hard proposition to prove either side: the pro side can and does argue that the solar wind monitors may have missed the feature that triggered the substorm, and the anti side can and does argue that a change in IMF direction is not sufficient to trigger a substorm.

I’m getting up in years now and have found my niche in Southern Thailand. While growing up I always had this mental “list” of things I wanted to see, do or experience and among walking the Great Wall of China, riding an elephant, sky diving and eating a Durian fruit, was seeing the Northern Lights.

Well, I’ve been blessed with having the opportunity to come darn close to ticking off everything on my list and one fateful night while driving home after work I saw the Northern Lights heading up the road in New Hampshire towards the little town of Rumney. At first I didn’t know what I was seeing…it just caught me unaware. But, once home I spend a good part of the night outside watching the Lights…beautiful and eerie…unexplainable really, their movements and sheen.

Sky diving just wasn’t in the cards for me and I’ll be taking a vacation up in Chang Mai, Northern Thailand this October, so I can tick off riding an elephant…but won’t be seeing those lights again…not this close to the equator!

Glad I had the opportunity to see the Northern Lights before I leave this world.

Having seen photos and video of aurora over the years it never occurred until now to me to ask why the bottom of the curtains/ribbons is so uniform in altitude. That seems to imply the charged particles are all roughly equally energetic, or perhaps that the density of the atmosphere is non-linear and the bottom of those ribbons is at an altitude where the density increases suddenly (which would also explain the apparently increased “density” of the ribbons at their lower edge). Can someone who knows comment?

@jam60 the colour of the emission is dictated by the atmospheric constituent. So very high up there is red, then there is the more commonly seen green, at the bottom of the green you can sometimes see a red border and a blue tint. The last two are hard to see with the naked eye. The particles are not equally energetic, they follow a distribution, often described (to simplify) as a Maxwellian, though it nearly always includes an energetic ‘tail’. You are right that the density of the atmosphere is important, the stopping distance increases such as it takes a bigger increase in energy to go a shorter distance. Rees (1989) from Cambridge university press is a good reference.

In terms of the IMF and substorm triggering, recent studies have suggested (using measurements closer to the magnetopause) that the most important factor is simply a period of predominantly southward IMF. Of course its more complicated than that since it the clock angle of the magnetic field that is really important plus interesting stuff can happen for other orientations.